PHOTOS: Grand Canyon fills with fog

Visitors to the Grand Canyon witnessed a rare sight this week: the canyon was overflowing with dense fog.

Called an inversion, it started last week.

"We are currently experiencing an after Thanksgiving treat. No, it's not more pumpkin pie. It's a once in a lifetime, outstanding, crazy, amazing, mind blowing inversion. Enjoy," the National Park Service posted on the Grand Canyon National Park's Facebook page.

Resembling a waterfall of dense fog, inversion clouds are created when cold air is trapped near the surface as warm air moves in above. The humidity in the colder air causes the fog.

A winter storm passed through the park the weekend before Thanksgiving, leaving the ground frozen and cold temperatures lingering.

The rangers and visitors were graced with a second inversion on Dec. 2.

There are smaller inversion events on occasion, but they usually come on cloudy days or only fill part of the canyon. The Nov. 29 inversion filled the entire canyon on a clear day. This usually only happens once a decade, Park Ranger Erin Whittaker told London's The Daily Mail.

The freezing fog left branches and trees overloaded with a ribbon-like icy coating. Rocks were coated with all kinds of icy patterns.

"Rangers wait for years to see it. Word spread like wildfire and most ran to the rim to photograph it. What a fantastic treat for all!" the rangers wrote on Facebook.

Visitors hoping to see into the deep depths of the natural marvel were not out of luck: the sun burned through the fog by the end of the day, revealing the canyon in all its glory.